A remarkable variety of clinical variables have been shown to be related to the body fat distribution. Many studies have shown that the waist hip ratio (WHR) is not only a simple index of the fat distribution pattern, but is also a powerful predictor of risk factors, diseases, and mortality. Despite extensive literature, systematic information on the distribution of values for the two components of the WHR (waist and hip circumference), for the ratio itself, and for changes in these values with change of weight is not available. The effects of age, sex and change in weight on WHR were examined in the BLSA subjects. Cross-sectionally, in men there was small increase in waist and small decrease in hip with increasing age, so that WHR increased by 0.001 per year of age. Although both waist and hip increased with age in women, the increase in waist was much larger than hip, so that the WHR increased by 0.002 per year of age. Longitudinally, weight change correlated positively with change of waist and hip in both sexes. In men change in waist was much larger than change in hip. In women change in hip was slightly larger than change in waist. On the average, these circumferential changes with weight result in large changes in WHR in men; in women the changes are rather proportional to the original ratio and only very small, generally insignificant, changes in the WHR occur.